1. Field
The following description relates to railway communication technology, and more particularly, to railway communication using wireless communication.
2. Description of the Related Art
Since railways began operating in 1830s England, various methods and apparatuses for securing the safety of trains have been developed and introduced. In communication between a train controller and an engineer or between engineers, a voice service is provided by analog or digital wireless communication equipment. However, recently, the existing railway signal equipment based on wired communication is quickly being replaced by wireless communication equipment, for reasons concerning compatibility between countries, economics, technology, etc.
A control scheme that has until now been performed via cable between ground equipment is being replaced, and control division of on-board ground equipment is being newly established from a functional perspective. Therefore, a safe and simple Communication Based Train Control (CBTC) system is being studied in various countries around the world, and has been put into practice in some countries. Also, with advancements in technology, the CBTC system is expected to be more broadly applied to railway signal systems than at present.
CBTC systems are installed on the ground and on board trains, and, by continuously performing communication therebetween, they ensure the safety of running trains. Such technology is the most advanced technology in signal control technology that has been developed to date, and shortens a running interval compared to conventional signal control systems, thus increasing a transport capacity. Also, data communication is performed between a train and a central control system so that running efficiencies of trains can be increased and the safety and convenience of railways can be optimized.
Some frequencies of the GSM band have been assigned as railway dedicated frequencies in ERTMS/ETC in Europe, and the wireless CBTC system uses GSM-R. Many countries including the USA use the IEEE 802.11.x standard of the Industrial Scientific Medical (ISM) 2.4 GHz band. Wireless communications between all CBTC systems used in Korea use the ISM 2.4 GHz band. Gimhae light rail, Metro Shinbundang line, and Yongin light rail, whose construction has been planned, as well as Metro Bundang line, plan to install a CBTC system using the ISM 2.4 GHz band.
However, in the RF-CBTC system using the 2.4 GHz band, it is difficult to ensure continuous performance due to interference caused by characteristic of the 2.4 GHz band, causing concern about possible interruption of railway operation. To overcome such limitations, there is need to secure a dedicated frequency for railway signals. Guidelines of the Korean Government advise that the ISM 2.4 GHz band cannot be used for services related to safety of life in a radio wave environment where a variety of wireless equipment is used. Moreover, technology standards of wireless equipment for businesses other than electronic communications (Notification No. 2007-80 of the Radio Research Laboratory) also state that the ISM 2.4 GHz band cannot be used to provide services related to life safety. Accordingly, when an accident occurs, a user of the frequency band may be held responsible.
In consideration of these circumstances in Korea regarding the 2.4 GHz band, interference may cause uncertainty in railway operation, and thus, for stable railway operation, there is a need to secure a railway dedicated frequency that enables safe railway traffic service and comfortable railway operation even when there is difficulty in a frequency allocation procedure and interval. In the future, railway operation will change to an unmanned driving system. To keep pace with change, as in countries with advanced rail systems, there is a need to secure frequency resources for building a railway safety system and an RF-CBTC system enabling advance preparation.
However, recently, since the amount of wireless data on the airwaves has been increasing explosively, it is not easy to assign many frequency domains for a railway dedicated frequency. In the future, demand for wireless frequency resources needed by railways is predicted to increase. However, in reality there is a limit to providing all needed frequencies in licensed frequency bands with limited frequency resources.